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PHYTOPHTHORA DISEASE OF GINSENG 



A THESIS 

Presented to the Faculty of the Graduate School 

of Cornell University for the degree of 

DOCTOR OF PHILOSOPHY 



BY 

JOSEPH ROSENBAUM 




Reprint of Cornell University Agricultural Experiment Station Bulletin 363. 

October, 1915. 



PHYTOPHTHORA DISEASE OF GINSENG 



A THESIS 

Presented to the Faculty of the Graduate School 

of Cornell University for the degree of 

DOCTOR OF PHILOSOPHY 



BY 

JOSEPH ROSENBAUM 



Reprint of Cornell University Agricultural Experiment Station Bulletin 363. 

October, 1915. 



Tn exchaag* 

FEB 4- 1916 






CONTENTS 

PAGE 

The host 65 

The disease 65 

Distribution 65 

History and economic importance 66 

Symptoms of the disease 66 

Symptoms of other diseases which may be confused with Phytophthora. . 70 

Alternaria blight 70 

Sclerotinia white rot : 70 

Sclerotinia black rot 71 

Acrostalagmus wilt 71 

Fusarium soft rot 71 

Etiology 71 

Early work on etiology 71 

Pathogenicity 72 

Identity of the organism 83 

Examination of literature 83 

Comparison of cultures 84 

Macroscopic growth on various media 84 

Kinds of spores produced on various media 85 

Comparative morphology 87 

Life history 89 

Morphology of the fungus 94 

Mycelium 94 

Conidiophores 95 

Conidia 95 

Germination of conidia 97 

Germination by germ tubes 97 

Germination by swarm spores 98 

Swarm spores 98 

Sexual organs 99 

Fertilization 100 

Oospore 1 00 

Oospore germination 100 

Control 102 

Spraying : 102 

Removal of diseased parts 103 

Deep planting 103 

Rotation of crops 103 

Sterilization of soil 104 

Drainage 104 

Bibliography 105 



63 



PHYTOPHTHORA DISEASE OF GINSENG 

Joseph Rosenbaum 1 
THE HOST 

The American ginseng, Panax quinque 'folium L., is a member of the 
family Araliaceas. It was brought under cultivation about twenty years 
ago, but either the same or a closely related species has been cultivated 
in Korea for more than two centuries. 

According to Jartoux (1714) 2 , ginseng is a native of the North Tem- 
perate Zone. It .grows in rich, damp soils, such as prevail in hardwood 
forests. The Chinese ginseng is found principally between the 126th 
and 136th meridians, east longitude. The American species has about 
the same range of latitude, but extends farther south. The natural 
environment of the plant indicates three factors as favorable to its growth, 
namely, shade, good drainage, and an acid soil. The failure of the grower 
to take these factors into consideration when removing the ginseng plant 
from its natural habitat to his gardens has been primarily responsible 
for most of his losses. 

In 1S21 (U. S. Secretary of the Treasury, 1822) 352,992 pounds of 
ginseng were exported from this country and sold for $171,786, an average 
of nearly 49 cents a pound. In 19 13 (U. S. Department of Commerce, 
19 1 4), the exports amounted to but 221,901 pounds. This was sold 
for $1,665,731, an average of about $7.50 a pound. This falling off in 
the number of pounds exported since the first shipments must be attributed 
in part to the diseases that attack this crop. It is becoming a common 
opinion among ginseng growers that the men who would grow ginseng 
successfully must first know all about the diseases to which the plant is 
subject. 

THE DISEASE 

DISTRIBUTION 

The disease known as mildew, Japanese mildew, or soft rot, attacks 
leaves, stems, and roots of the host. In this country it probably exists 
in every State in which ginseng is grown — Washington, Oregon, Nebraska, 
Kansas, Minnesota, Missouri, i\rkansas, Wisconsin, Michigan, Indiana, 
Ohio, New York, Pennsylvania, New Jersey, and Maryland. It is de- 
structive in Japan also, where it was first reported by Hanai (1900). It is 
known there as Koshi-ore, meaning bending at the loins. 

' In making these investigations, the author had the cooperation of W. A. Orton, in charge of Cotton 
and Truck Disease Investigations, United States Bureau of Plant Industry. The author wishes to 
acknowledge also the many suggestions received during the progress of the work from Di. Donald Reddick 
and Professor H. H. Whetzel, of the Department of Plant Pathology, Cornell University. 

2 Dates in parenthesis refer to bibliography, page 105. 

65 



66 



Bulletin 363 



HISTORY AND ECONOMIC IMPORTANCE 

Hori (1907), who was the first to study this disease rather carefully, 
states that it has long been known to Japanese ginseng growers. In the 
United States the disease was first discovered on ginseng in the State 
of Ohio by J. M. van Hook (1906), and it has since been observed more 
or less commonly in the ginseng-growing regions of the United States. 
Because of its general occurrence in ginseng gardens in many States, and 
the fact that it attacks all parts of the plant, both above and below the 
ground, it forms one of the most serious disease problems that confront 
the grower. 




PHOTOGRAPH BY WHETZEL 

FlG. 2. CHARACTERISTIC SYMPTOM OF GINSENG MILDEW 
One or more leaflets droop and hang limp and shriveled 

Hori (1907) reports a loss of $25,000, due to the disease, in one prov- 
ince of Japan in the spring of 1904. From observations by the writer 
in ginseng gardens for the past four summers, it is safe to say that in the 
eastern United States from twenty to thirty per cent of the plants are 
lost through the attacks of the disease before they reach the age of five 
or six years. 

SYMPTOMS OF THE DISEASE 

The tops of the plants are affected in a characteristic manner. Usually 
there is a drooping of a single one or all of the leaflets at the top of the 



Phytophthora Disease of Ginseng 



67 



petiole (Fig. 2). It happens in many cases that the disease attacks the 
main stem at the crown, or point where the leaf petioles are attached, 
and all the leaves droop and hang limp from the top of the stem (Fig. 3). 
Some other ginseng diseases exhibit similar symptoms, and microscopic 




Fig. 3. symptom of ginseng mildew in late stage 

The stage here shown is much later than that shown in figure 2. All the leaflets hang shriveled 

and dry 



examination and identification of the causal organism is often necessary 
in order to determine definitely what disease is present. The tissues 
at the point of infection are rapidly injured and lose their turgidity, 
and the leaflets hang limp from the petiole. 



68 



Bulletin 363 



The leaf blades also show characteristic lesions or spots. The spots 
appear dark green and water-soaked, much like those of the Alternaria 
blight in its early stages. A week or two after the first appearance of 
the spot, the center becomes white, the margins remaining a dark water- 
soaked green. The spots vary in size from one centimeter in diameter 
to lesions involving the entire leaf. The demarcation between diseased 
and healthy tissue is not sharply defined. The spotting shows on both 
sides of the leaf, but in general the differently colored regions within 
the spot are better shown on the upper surface (Fig. 4). 




Fig. 4. lesions of ginseng mildew on leaves 

The water-soaked margin of the lesion, particularly in the leaflet at the right, should be noted 

In the early stages of the disease, especially on the. stalk or the petiole, 
the surface of the affected parts may show an almost indiscernible silvery 
white coating. During periods of sunshine the diseased tissues dry up 
quickly, leaving the dead and shriveled leaves at the top of the stem. 
Under such conditions the disease does not spread down the stem with 
great rapidity. If atmospheric conditions remain moist and cloudy, 
the entire stalk is gradually involved. On pressing a diseased stalk 
between thumb and forefinger it is found that, in contrast with the 
ordinarily firm stalk, the diseased one is hollow. The hollowing of the 
stem is preceded by a watery discoloration of the tissues. 



Phytophthora Disease of Ginseng 



69 



The roots may be attacked, showing a semi-soft rot. The lesion may- 
start at any point on the root and in a short time involve all the tissues. 
When such roots are allowed to remain in the soil for any considerable 




Fig. 5. SYMPTOM OF ginseng mildew on root 

The two roots have been cut longitudinally and show external and internal appearance. The root on 
the right was kept in a moist chamber for two days, and the external view shows well the growth of 
mycelium on the surface 

time, various organisms, such as Fusaria and bacteria, invade the diseased 
tissues, causing them to become soft. At this stage the disease is often 
accompanied by a disagreeable odor characteristic of vegetable decays. 



yo Bulletin 363 

In some cases the disease starting in the root spreads up the stem. Roots 
cut longitudinally, showing the characteristic rotting, are illustrated in 
figure 5. 

When the disease originates in the root and does not extend rapidly 
into the stem, the leaves may take on various shades of yellow and red, 
resembling the colors that they naturally assume toward the close of the 
growing period. Such ' discoloration of the tops in the early part of the 
season, however, while indicating some pathological condition, is not 
to be associated necessarily with the Phytophthora rot. Any disturbance 
in the functions of the root may cause such discoloration, and this condition 
may occur in the case of other rots, as, for example, the Sclerotinia white 
rot (Sclerotinia libertiana Fckl.). 

SYMPTOMS OF OTHER DISEASES WHICH MAY BE CONFUSED WITH PHYTOPHTKORA 

The symptoms of a number of other ginseng diseases may be confused 
with those of the Phytophthora disease. Such are the Alternaria blight, 
the Sclerotinia white rot, the Sclerotinia black rot, the Acrostalagmus 
wilt, and an undescribed fusarial rot. 

ALTERNARIA BLIGHT 

Alternaria blight is a very widespread disease caused by a fungus of 
the genus Alternaria, designated by Whetzel as species panax, although 
a technical description has not been published. It attacks stems, leaves, 
and roots of the host. The first symptoms in the spring appear as dark 
brown cankers on the stem near the surface of the soil. The spots on the 
leaves are similar in size to those caused by Phytophthora, but may be 
distinguished from the spotting caused by the latter in that they exhibit 
a broad, rusty brown border. The Alternaria lesions may also appear 
on the top of the plant as the point where the leaflets are attached to the 
petiole or where the petioles arise at the top of the stem, as in plants 
affected with the Phytophthora disease. The lesions are, however, 
readily distinguished from those of Phytophthora in that they exhibit 
a velvety brown coating at the point of attack. The Alternaria disease 
also occurs on the roots in the form of a dry rot. The tissues of the root 
are shrunken, and are darker in color and firmer to the touch than roots 
affected by Phytophthora. 

SCLEROTINIA WHITE ROT 

Inoculation experiments have proved that the disease known as 
Sclerotinia white rot is caused by Sclerotinia libertiana Fckl. Affected 
plants wilt and sometimes fall over. This is due to a rotting of the stem 
at its base, which usually involves also the crown of the root. The roots 



Phytophthora Disease of Ginseng 71 

become very soft and watery, but non-elastic. When placed in a moist 
chamber, an affected root invariably becomes covered with the white 
felt of the vegetative growth of the fungus. After a time numerous 
black sclerotia appear. 

sclerotinia black rot 
The cause of the disease known as Sclerotinia black rot is Sclerotinia 
panaris Rankin. 3 The roots only are affected. When the disease is in 
an advanced stage the entire root, as the name indicates, is coal black. 
In the earlier stages the rot is in all external symptoms similar to that of 
Phytophthora; any dissimilarity before the root has turned black can 
be detected only by the aid of a microscope. Sections through tissue 
affected with the black rot disease show an abundance of dark brown 
mycelium. 

ACROSTALAGMUS WILT 

The disease known as Acrostalagmus wilt is said by van Hook (1904) 
to be caused by a species of Acrostalagmus. The roots are the only parts 
attacked. The first external symptom is a wilting of the tops. The 
leaves finally become dry and papery to the touch. The limp appearance 
of the top at once suggests the possibility of a lack of moisture in the 
soil. Externally the roots show no lesions, but cross sections of affected 
roots exhibit to the naked eye a brown ring in the region of the sap tubes. 

FUSARIUM SOFT ROT 

The disease called Fusarium soft rot is caused by a species of Fusarium 
and is the most likely of these diseases to be confused with Phytophthora 
rot of roots. Roots attacked by the Fusarium are softer, however, and 
are always accompanied in the last stages by a strong odor. 

ETIOLOGY 

The cause of the Phytophthora disease of ginseng is a fungous parasite, 
Phytophthora cactorum (Cohn et Leb.) Schrot. The genus Phytophthora 
was founded by de Bary (1876) on the potato blight fungus, P. injestans. 
The genus as it now stands includes more than a dozen species. 

EARLY WORK ON ETIOLOGY 

The history of the study of the organism associated with the disease 
can be summed up as follows: Hanai (1900:28) and Hori (1907:153) 
demonstrated the constant association of the Phycomycete with the 
lesions of the ginseng leaves. Hori, in the article cited, makes the following 
statement: " Since this decaying process proceeds downward to the 

3 Recent inoculations indicate that Sclerotinia panaris Rankin is probably identical with Sclerotinia 
smilarina Durand. 



72 Bulletin ^63 

roots, the entire plant begins to wilt and drops to the ground." No 
experimental evidence is furnished to show that the roots really rot, or 
that when this does occur it is due to the attacks of Phytophthora. Van 
Hook (1906) reports the constant presence of oospores of the same fungus 
in the stems of ginseng. Whetzel (19 10) appears to be the only one 
who has done any work on the pathogenicity of the fungus previous to the 
studies herein presented. In 1909 he made a series of inoculations, 
employing pure cultures of the Phytophthora isolated from ginseng, 
and reports that " in every case there was prompt infection, with the 
resulting lesions characteristic of the disease." Little stress is laid, 
however, on the Phytophthora causing injury to the roots. In a bulletin 
by Whetzel and the writer (19 12) the following statement is made: 
" Observations in the gardens show that the roots of plants, the tops 
of which are killed by the mildew, invariably rot unless promptly removed 
and dried." 

For the past four seasons the writer has been investigating the diseases 
of ginseng, studying for the most part the root rots. During the course 
of the work it has developed that a large proportion of the soft rot is 
due to Phytophthora. This bulletin presents a study of the life history 
and identity of Phytophthora as it exists on ginseng. 

PATHOGENICITY 

Several methods have been employed for isolating the fungus and 
growing it in pure culture. In 19 14 the organism was obtained from 
roots sent from a number of places — Ithaca, Scott, and Alden (New 
York), Kutztown (Pennsylvania), Mentor (Ohio), and Cassopolis (Michi- 
gan) . Isolation from diseased roots was successful only when made from 
roots on which the disease had just started. Later the lesion is invaded 
by other soil organisms to such an extent that isolation of Phytophthora 
is difficult or impossible. 

In most cases in which the fungus was isolated directly from the root, 
bits of tissue from the inside of the root at the junction of the healthy 
and the diseased areas were placed in tubes of oat agar. In some cases 
isolations were made directly from the root by placing the root in a moist 
chamber and carefully transferring to bean pod plugs the surface growth 
of mycelium which appeared in from two to three days. 

Pure cultures of the fungus are obtained most readily, not from the 
roots, but from the stems. The method of procedure is as follows: 
Diseased stems are immersed in a 1-1000 solution of mercuric chloride 
for from two to three minutes, the stems are split longitudinally, and 
tissue plantings are made on poured plates of oat or bean agar. In three 
or four days the fungus usually will have grown out from the bits of tissue, 



Phytophthora Disease of Ginseng 73 

and subcultures can be made to test tubes of oat or potato agar. Good 
results may also be obtained, in case the disease is in its early stages, 
by washing the stems in mercuric chloride and placing them in a moist 
chamber. Conidia of the fungus usually appear within a period of from 
twenty-four to thirty-six hours. Transfers made from the surface growth 
usually give pure cultures. 

When the fungus is obtained in pure cultures it grows readily on a 
number of media. The writer has grown it on oat agar as made by 
Clinton, on Thaxter's hard potato agar, on corn meal agar, on sterilized 
ginseng stems, ,on a ginseng decoction, on bean pods, and on lima bean 
agar. 4 The growth on synthetic media has been very slight. 

After the ginseng fungus was isolated and grown in pure culture it 
was used for inoculating healthy plants. The experiments in inoculation 
of the tops have extended over a period of four years, but it was only 
in the spring of 19 13 that inoculation of the roots was attempted. 

Inoculation of the tops was made in the following ways: (1) The 
stems and leaves were sprayed with a water suspension of conidia and 
swarm spores, an atomizer being used for the spraying. The plants were 
covered with a bell jar for four or five days. Check plants were treated in 
a similar manner, with the exception that conidia were not added to the 
water. (2) By means of a platinum needle a bit of the fungus was removed 
from a pure culture and placed in the crotch of the plant. The inoculum 
was covered with moist cotton. For checks, the crotches of other plants 
were likewise covered with moist cotton. (3) By the use of a flamed scalpel 
a slight injury was made in the crotch of the plant and the inoculum 
was placed in the cut. 

Inoculation of the roots was made in the following ways: (1) The soil 
was removed from one side of the root. The root was slightly cut with 
a flamed scalpel and a bit of a pure culture of the fungus was placed in 
the cut. The checks were treated in a similar manner, but no fungus was 
placed in the cut. All the roots were then covered with soil. (2) Roots 
were placed in pots and were inoculated by watering with a solution 
containing conidia of the fungus. Previous to inoculation certain roots 
were punctured with a flamed needle. As checks, similarly treated 
roots were kept moist with water not containing the fungus. (3) Freshly 
dug roots were immersed in a solution of mercuric chloride for ten minutes, 



4 The media used were composed as follows: 

Hard potato agar: 200 grams of potato, 20 grams of glucose, and 30 grams of agar, for every 1000 
cubic centimeters of water. 

Oat agar was made according to the directions given by G. P. Clinton in the Report of the Connecticut 
Agricultural Experiment Station for 1909 and 1910, page 760. 

Corn meal agar was made according to the formula given by C. L. Shear and Anna K. Wood in Bulletin 
252 of the United States Bureau of Plant Industry, page 15. 

Lima bean agar: 100 grams of ground lima beans and 15 grams oi agar for every 1000 cubic centi- 
meters of water. 

Bean pods: pods of ordinary string beans placed in test tubes with a small quantity of water and sterilized. 



74 



Bulletin 363 



rinsed several times with sterile water, and placed in sterile test tubes. 
The inoculation was made in the test tube in much the same way as a 
subculture is made. The roots in the test tube were cut with a flamed 
scalpel. By means of a platinum needle bits of the pure culture were 
inserted into the cuts. The checks were likewise injured with the flamed 
scalpel, but no fungus was placed in the cuts. The test tubes were then 
placed in a moist chamber for from two to three days. Later this was 
found to be unnecessary. 

Results of inoculations on tops, on roots placed in the soil, and on 
roots placed in test tubes, are shown in figures 6, 7, and 8. It should 




Fig. 6. ginseng plants inoculated with a pure culture of phytophthora 

cactorum 



be stated here that when plants were injured, either on the tops or on 
the roots, a higher proportion of infection was obtained than when the 
tissues were not injured. As far as root rot in the garden is concerned, 
however, this makes very little difference, for one seldom finds a root 
in the soil without some injury due to rodents, insects, transplanting, 
or other causes. 

In all the inoculation work, in addition to the ginseng Phytophthora 
a culture marked Phytophthora cactorum was used. The latter was 
isolated by D. L. Peters, of Berlin, from Phyllocactus. This culture 
was found to be as pathogenic to ginseng as the Phytophthora isolated 
from ginseng. 



Phytophthora Disease of Ginseng 



75 



An attempt was made to determine whether the use of the different 
organs of the fungus for inoculating — mycelium, conidia, or oospores — 
made any difference in the ability to 
produce infection. These various organs 
were obtained from pure cultures of 
different ages and from different media. 
The mycelium was obtained from very 
young cultures on hard potato agar; the 
conidia were obtained from older cultures 
on the same medium, also from corn 
meal agar; the oospores, from old cultures 
on bean pods. No doubt mycelium was 
present in every case. No difference in 
ability to infect was found. The period 

of incuba- 
tion — ■ that 

is, from the 

time when 

the parasite 

is placed on 

the host to 

the time 

when the 

first visible 

FlG. 7. GINSENG ROOTS INOCULATED 

symptoms W i T h a pure culture of phytoph- 
appear — is thora cactorum 

r ,1 Growing roots two years old were slit with 

trom tnree a scalpel and inoculated with a pure culture 

, r- 1 of Phytophthora cactorum. The root on the 

tO nve QayS left was treated similarly but was not inccu- 

1 1 lated. The inoculations were made on 

Oil rOOtS ana. August 4, 1913; the photograph was made 

from four to seven days later 
six days on tops. 

The length of time during which the 
fungus has been in artificial cultures does 
not seem to have any appreciable effect on 
its virulence. One culture isolated in the 
summer of 191 1 was employed, and another 
isolated in the spring of 19 13. They gave 
almost identical results in all the inoculation 
work. Wherever the rot was produced, it 
was always possible to make re-isolations by 
cutting out pieces of tissue at the boundary between the healthy 
and the diseased regions, and planting these on oat agar or bean pod 





Fig. 8. ginseng roots inocu- 
lated WITH A PURE CULTURE 
OF PHYTOPHTHORA CACTORUM 

Two-years-old roots of ginseng were 
disinfected, placed in sterile test 
tubes, and inoculated with a pure 
culture of Phytophthora cactorum. 
The root on the left was treated simi- 
larly but was not inoculated. The 
inoculations were made on May 15, 
1013; the photogtaph was made ten 
days later 



76 Bulletin 363 

plugs. In a few instances the re-isolations were made by placing 
the rotted root in a moist chamber and then making plantings on 
oat agar from the mycelium appearing on the surface. Re-isolations 
from the tops were made by washing the stems for from two to three 
minutes in a 1-1000 solution of mercuric chloride, cutting them length- 
wise, and making plantings from the interior on oat agar. The fungus 
obtained from such re-isolations was identical with the original culture, 
as regards both morphology, behavior on culture media, and ability 
to produce the disease. Koch's rules of proof were carried out for the 
Phytophthora isolated from ginseng, and also for Phytophthora cactorum 
from Phyllocactus. 

In 1913 inoculations were made as shown in table 1. The percentage 
of infection obtained in all these inoculations leaves no doubt as to the 
conclusions to be reached. In 19 14 a greater number of inoculations 
were made and the results obtained were almost identical with those 
of 1913. 



TABLE 1. 



Inoculations Made in Various Ways with Phytophthora cactorum 
from Phyllocactus and from Ginseng. Summer of 1913 



Date 


Source of 

organism 

used 


Condition 

of plants 

at time of 

inoculation 


Manner of 
inoculation 


Number 
of plants 
inocu- 
lated* 


Percent- 
age of in- 
fection* 


Number 

of plants 

used as 

checks f 


April 19 


Phyllocactus 
and ginseng 


Four years 
old, begin- 
ning to push 
through soil 


Tops sprayed 
with sus- 
pension 
of spores 


3 


66.6 


1 


April 19 


Phyllocactus 
and ginseng 
1911 


Same as 
above 


Plants not 
injured, 
inoculum 
placed in crotch 


3 
3 


33-3 p -t 
66.6G.J 


1 


April 19 


Phyllocactus 
and ginseng 
1911 


Same as 
above 


Plants slightly 
injured, 
inoculum 
placed in crotch 


3 
3 


1 00.0 P. 
66. 6G. 


1 


April 19 


Phyllocactus 
and ginseng 
191 1 


Same as 
above 


Soil removed, 
root injured, 
in< iculum placed 
in injury 


4 


100. 




April 19 


Phyllocactus 
and ginseng 
1911 


Same as 
above 


Roots in test 
tubes 


3 


100. 


2 



*The number of plants inoculated and the percentage of infection are the same for Phyllocactus and for 
ginseng unless otherwise stated. 

t All checks remained healthy unless otherwise stated. 

t"P." indicates percentage for Phyllocactus; "G.," percentage for ginseng. 



Phytophthora Disease of Ginseng 



77 







Table i 


(continued) 








Date 


Source of 

organism 

used 


Condition 

of plants 

at time of 

inoculation 


Manner of 
inoculation 


r 

Number 
of plants 
inocu- 
lated* 


Percent- 
age of in- 
fection* 


Number 

of plants 

used as 

checks f 


April 19 


Phyllocactus 
and ginseng 
1911 


Same as 
above 


Roots placed in 
pots and 
watered with a 
suspension of 
inoculum 


3 







April .19 


Phyllocactus 
and ginseng 
1911 


Same as 
above 


Same as above, 
but roots 
pricked 


3 
3 


66.6P.J 

33 3G.J 


1 


April 20 


Phyllocactus 
and ginseng 
191 1 


Same as 
above 


Roots in test 
tubes 


3 


100. 


2 


April 20 


Phyllocactus 


Same as 
above 


Tops sprayed 
with a 

suspension of 
inoculum 


3 


33-3 


1 


April 20 


Phyllocactus 


Same as 
above 


Plants injured, 
inoculum 
placed in crotch 


3 


100. 


2 


April 20 


Phyllocactus 


Same as 
above 


Soil removed, 
root injured, 
inoculum 
placed in 
injury 


3 


100. 


2 


April 20 


Phyllocactus 


Same as 
above 


Roots in test 
tubes 


3 


100. 


1 


April 20 


Phyllocactus 


Saine as 
above 


Same as above, 
but roots 
pricked 


3 





2 


May 16 


Phyllocactus 
and ginseng 
1911 


Five years 
old, full- 
grown in 
garden 


Inoculum 
placed on 
leaves in drops 
of water 


3 


100. 


1 


May 16 § 


Phyllocactus 


Same as 
above 


Same as 
above 


3 


1 00.0 


1 


May 27 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above 


3 
3 


1 00.0 P. 
66 . 6G. 


1 


May 27 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Tops sprayed 
with a 

suspension of 
inoculum 


4 
4 


75. oP. 
100.0G. 


1 



* The number of plants inoculated and the percentage o' infection are the same for Phyllocactus and for 
ginseng unless otherwise stated. 

t All checks remained healthy unless otherwise stated. 

t "P." indicates percentage for Phyllocactus; "G.," percentage for ginseng. 

§ Inoculations were made on the same day as the preceding ones, but either in a different garden or in 
a different part of the same garden. 



Bulletin 363 
Table i (continued) 



Date 


Source of 

organism 

used 


Condition 

of plants 

at time of 

inoculation 


Manner of 
inoculation 


Number 
of plants 
inocu- 
lated* 


Percent- 
age of in- 
fection * 


Number 

of plants 

used as 

checks f 


May 27 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Plants slightly 
injured, 
inoculum 
placed in crotch 


4 


1 00.0 


2 


May 27 Phyllocactus 
and ginseng 
1913 


Same as 
above 


Soil removed, 
root injured 
and inoculated 


4 


100. 


2 


May 27 


Phyllocactus 
and ginseng 
1913 


Same as 
above, but 
with roots 
removed 


Roots in test 
tubes 


4 
4 


75-oP.t 
ioo.oG.f 


2 


May 27 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Roots placed 
in pots and 
watered with a 
suspension of 
inoculum 


3 





1 


May 27 


Phyllocactus 
and ginseng 
1913 


Same as 
above, with 
roots pricked 


Same as above 


3 





1 


June 13 


Phyllocactus 
and ginseng 
1911 


Four years 
old, roots 
removed 
from garden 


Roots in test 
tubes 


4 


1 00.0 


1 


June 13 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above 


4 


100. 


1 


June 13 


Phyllocactus 


Same as 
above 


Same as above 


4 


roo.o 


1 


June 13 


Phyllocactus 
and ginseng 
1911 


Four years 
old, plants 
standing in 
garden 


Soil removed, 
root injured 
and inoculated 


3 


100. 


1 


June 13 


Phyllocactus 
and ginseng 


Same as 
above 


Same as above 


3 


100. 


1 


June 13 


Phyllocactus 


Same as 
above 


Same as above 


3 


100. 


1 


June 14 


Phyllocactus 
and ginseng 
1911 


Same as 
above 


Plants slightly 
injured in 
crotch and 
inoculated 


3 


100. 


1 



*The number of plants inoculated and the percentage of infection are the same for Phyllocactus and for 
ginseng unless otherwise stated. 

t All checks remained healthy unless otherwise stated. 

% "P." indicates percentage for Phyllocactus; "G.," percentage for ginseng. 



Phytophthora Disease of Ginseng 
Table i (continued) 



79 



Date 


Source of 

organism 

used 


Condition 

of plants 

at time of 

inoculation 


Manner of 
inoculation 


Number 
of plants 
inocu- 
lated * 


Percent- 
age of in- 
fection* 


Number 

of plants 

used as 

checks f 


June 14 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above 


3 


100. 


1 


June 14 


Phyllocactus 


Same as 
above 


Same as above 


3 


100.0 


1 


June 14 


Phyllocactus 
and ginseng 
1911 


Same as 
above 


Soil removed, 
root uninjured, 
inoculum 
placed on 
surface 


4 

4 


25.0P4 

oG.J 


1 


June 14 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above 


4 





1 


June 14 


Phyllocactus 


Same as 
above 


vSame as above 


4 





1 


July 1 iPhyllocactus 
and ginseng 
1911 


Five years 
old, plants 
standing in 
garden 


Tops sprayed 
with a 

suspension of 
inoculum 


3 
3 


33-3P- 
100.0G. 


1 


July I Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above 


3 


66.6 


1 


July 1 Phyllocactus 


Same as 
above 


Same as above 


3 


66.6 


1 


July 1 


Phyllocactus 
and ginseng 
1911 


Same as 
above 


Inoculum 
placed on 
uninjured 
leaves 


3 


100. 


1 


July 1 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above 


3 


100. 


1 


July 1 


Phyllocactus 


Same as 
above 


Same as above 


3 


100. 


1 


July 1 


Phyllocactus 
and ginseng 
1911 


Same as 
above 


Soil removed, 
root injured 
and inoculated 


4 


100. 


1 


July 1 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above 


4 


100.0 


1 



* The number of plants inoculated and the percentage of infection are the same for Phyllocactus and for 
ginseng unless otherwise stated. 

t All checks remained healthy unless otherwise stated. 

t "P." indicates percentage for Phyllocactus; "G.," percentage for ginseng. 



8o 



Bulletin 363 
Table i (continued) 



Date 


Source of 

organism 

used 


Condition 

of plants 

at time of 

inoculation 


Manner of 
inoculation 


Number 
of plants 
inocu- 
lated* 


Percent- 
age of in- 
fection * 


Number 

of plants 

used as 

checks f 


July 1 


Phyllocactus 


Same as 
above 


Same as above 


4 


100. 


1 


July 1 


Phyllocactus 

and ginseng 
1911 


Five years 
old, roots 
removed 
from garden 


Roots in test 
tubes 


4 


1 00.0 


1 


July 1 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above 


4 


100. 


1 


July 1 


Phyllocactus 


Same as 
above 


Same as above 


4 


1 00 . 


1 


July 16 


Phyllocactus 
and ginseng 
1911 


Three years 
old, plants 
standing in 
garden 


Plants slightly 
injured, 
inoculum 
placed in crotch 


3 


100. 


1 


July 16 


Phyllocactus 
and ginseng 
19 1 3 


Same as 
above 


Same as above 


3 


100. 


1 


July 16 


Phyllocactus 
and ginseng 
1911 


Same as 
above 


Roots not 
injured, 
inoculum 
placed on 
surface 


3 





1 


July 16 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above 


3 





1 


July 16 


Phyllocactus 


Same as 
above 


Same as above 


3 





1 


August 1 


Phyllocactus 
and ginseng 
1911 


Four years 
old, plants 
standing in 
garden 


Soil removed, 
root injured 
and inoculated 


4 
4 


75-oP.t 

100. oG. % 


1 


August 1 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above 


4 


100. 


1 


August 1 


Phyllocactus 


Same as 
above 


Same as above 


4 


100. 


1 


August 1 


Phyllocactus 
and ginseng 
1911 


Four years 
old, roots 
removed 
Tom garden 


Roots 

disinfected and 
placed in test 
;ubes 


3 


100. 


1 



* The number of plants inoculated and the percentage of infection are the same for Phyllocactus and for 
ginseng unless otherwise stated. 

t All checks remained healthy unless otherwise stated. 

X "P." indicates percentage for Phyllocactus; "G.," percentage for ginseng. 



Phytophthora Disease of Ginseng 
Table i (continued) 



Date 


Source of 

organism 

used 


Condition 

of plants 

at time of 

inoculation 


Manner of 
inoculation 


Number 
of plants 
inocu- 
lated* 


Percent- 
age of in- 
fection* 


Number 

of plants 

used as 

checks t 


August I 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above 


3 


100. 


1 


August i 


Phyllocactus 


Same as 
above 


Same as above 


3 


100. 


1 


August i 


Phyllocactus 
and ginseng 
191 1 


Four years 
old, plants 
standing in 
garden 


Plants injured, 
inoculum 
placed in crotch 


4 


100. 


1 


August i 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above 


4 


100. 


i 


August i 


Phyllocactus 


Same as 
above 


Same as above 


4 


100. 


1 


August 15 


Phyllocactus 
and ginseng 


Same as 
above 


Plants not 
injured, 
inoculum 
placed in crotch 


4 





1 


August 15 


Phyllocactus 


Same as 
above 


Same as above 


4 





1 


August 15 


Phyllocactus 
and ginseng 


Three years 
old, plants 
standing in 
garden 


Tops sprayed 
with a 
suspension 
of inoculum 


3 





1 


August 1 5 


Phyllocactus 


Same as 
above 


Same as above 


3 





1 


September 3 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Roots not 
injured, 
inoculum 
placed on 
surface 


4 





1 


September 3 


Phyllocactus 


Same as 
above 


Same as above 


4 





1 


September 3 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Roots injured, 
inoculum 
placed on 
surface 


3 


1 00.0 


1 


September 3 


Phyllocactus 


Same as 
above 


Same as above 


3 


100. 


1 



* The number of plants inoculated and the percentage of infection are the same for Phyllocactus and for 
ginseng unless otherwise stated. 

t All checks remained healthy unless otherwise stated. 



82 



Bulletin 363 
Table i (concluded) 



Date 


Source of 

organism 

used 


Condition 

of plants 

at time of 

inoculation 


Manner of 
inoculation 


Number 
of plants 
inocu- 
lated* 


Percent- 
age of in- 
fection* 


Number 

of plants 

used as 

checks f 


September 3 


Phyllocactus 
and ginseng 
1913 


Three years 
old, roots 
removed 
from garden 


Roots placed in 
pots and 
watered with a 
suspension 
of inoculum 


3 





1 


September 3 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above, 
but roots 
pricked 


3 





1 


September 3 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Roots 

disinfected and 
placed in test 
tubes 


4 
4 


50.0P.J 
ioo.oG.j 


1 


September 3 


Phyllocactus 


Same as 
above 


Same as above 


4 


50.0 


1 


October 2 


Phyllocactus 
and ginseng 
1913 


Four years 
old, roots 
removed 
from garden 


Same as above 


3 


100. 


1 


October 2 


Phyllocactus 


Same as 
above 


Same as above 


3 


100. 


1 


October 2 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Roots placed in 
pot, injured, 
inoculum 
placed on 
surface 


3 


100. 


1 


October 2 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above 
but not injured 


3 


100. 1 


October 2 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Roots placed in 
pot and 
watered with a 
suspension 
of inoculum 


3 





1 


October 2 


Phyllocactus 
and ginseng 
1913 


Same as 
above 


Same as above, 
but roots 
pricked 


3 

3 


33 3 P- 
oG. 


1 



* The number of plants inoculated and the percentage of infection are the same for Phyllocactus and for 
ginseng unless otherwise stated. 

t All checks remained healthy unless otherwise stated. 

j "P." indicates percentage for Phyllocactus; "G.," percentage for ginseng. 



Phytophthora Disease of Ginseng 83 

identity of the organism 
examination of literature 

A careful examination of the fungus from pure culture on various 
media shows that it resembles most closely Phytophthora cactorum (Cohn 
et Leb.) Schroeter (1889). Saccardo (1888) lists as synonyms of this 
species the following: Peronospora cactorum Cohn et Leb., P. Fagi 
Hartig, P. Semperuivi Schenk, Phytophthora omnivora de Bary. It may 
be well to briefly review here the history of the species. 

Lebert and Cohn (1870) observed a rot on Cereus giganteus and Melo- 
cactus nigrotomentosus . From their description of the symptoms it appears 
that the nature of the disease was a dissolution and separation of the 
individual cells, resulting in a more or less soft rot. An abundance of 
mycelium, conidia, and oospores was found. From the nature of the 
fungus Lebert and Cohn rightly determined that it was a Phycomycete, 
and described it as Peronospora cactorum. As far as they could deter- 
mine, haustoria were lacking. 

Hartig (1876:121) describes a fungus, Peronospora Fagi, as causing a disease 
of beech. A similar fungus was described the previous year by Schenk 
(1875), under the name Peronospora Sempervivi, found by him to be 
causing a disease of Sempervivum. De Bary (1881), in order to settle 
the identity of these forms — which he held to be identical — with little 
regard for priority or rules of nomenclature gave them collectively the 
name Phytophthora omnivora. Hartig (1882:42) wrote as follows in com- 
menting on this change: " I accept this new name, since it behooves me 
above everything else to desire a name for the parasite that shall bear no 
false significance. Since I have, from the earliest time, observed that the 
disease attacks maple, pine, larch, and fir, I believe omnivora is- better 
deserved than Fagi. In opposition to many systematists of later times 
who from their researches on priority have changed the customary name for 
another never accepted as valid by the science of the past one hundred 
years, I have been of the opinion that names existed, not for the authors, 
but for the scientific public." 5 

De Bary was aware of the work of Cohn and Lebert when he 
wrote that there was not a doubt in his mind that the two forms were 
identical. He proposed the specific name omnivora as better expressing 
the nature of the organism. Schroeter (1889:236), recognizing the work 
of Cohn and Lebert, adopted the original specific name cactorum and 
simply classed the fungus in the more recently formed genus. The 
name as it stands, therefore, is Phytophthora cactorum (Cohn et Leb.) 
Schroeter. 



f Translation from the German. 



8| Bulletin 363 

Syn. Peronospora cactorum (Cohn et. Leb.). Bietr. biol. pflanz. 1 : 51-57. 1870. 
Peronospora Sempervivi Schenk. Bot. ztg. 33:690-693. 1875. 
Peronospora Fagi Hartig. Zeitsch. forst.- u. jagdw. 8:117-123. 1876. 
Phytophthora omnivora De Bary. Bot. ztg. 39:585-595, 601-609, 617-626. 1881. 
Phytophthora cactorum (Cohn et Leb.) Schroeter. Krpyt-fl. Schlesien 3:235- 
236. 1889. 

The following is the original description as given by Lebert and Cohn 
(1870): 

" Mycelii tubi graciles nonnunquam torulosi ramosi, ramis angulo 
recto patentibus, haustoriis destituti. Stipites conidiophori tenues, in 
modum cincinni unilateraliter pauce-ramosi, sub apicibus ramorum coni- 
diferis non raro vesiculoso-inflati. Conidia in stipitibus pauca hyalina, 
ellipsoidea vel ovata, apice papilla prominente munita majuscula = 
0,048 mm. (1/28-1/15 mm.). 

" Oogonia conglomerata membrana tenui marcescente munita, singula 
oosporam singulam exacte globosam episporio valido luteo-fusco pellucido 
laevi praeditam foventia, diametro = 0,024 mm. (1/40 mm.). 

" Habitat in meatibus intercellularibus parenchymatis variorum Cac- 
torum quorum morbum putredine quadam finitum efficit. Observ. 
hieme 1 868-1 869 in viridario excellentissimi ducis a Jacobi Vratislaviae. " 

Unfortunately it has thus far been impossible for the writer to examine 
the type material or to make isolations from the original host, and he is 
compelled to rely entirely on the above description and the descriptions 
of the later workers for the identity of this fungus. For comparison, 
a culture marked Phytophthora cactorum was obtained from the Bureau 
pour le Distribution de Cultures de Moisissures, of the International 
Association of Botanists in Amsterdam, with the information that it 
was isolated from Phyllocactus by D. L. Peters, of Berlin. 

COMPARISON OF CULTURES 

Since the Phytophthora of ginseng resembles the culture marked Phy- 
tophthora cactorum, a detailed comparison is here given. 6 

MACROSCOPIC GROWTH ON VARIOUS MEDIA 

Phytophthora from ginseng and Phytophthora cactorum from Phyllo- 
cactus were grown on hard potato agar, oat agar, corn meal agar, bean 
pod plugs, and sterilized ginseng stems. Various synthetic media were 
also employed, but the growth on these was so small a^ to make them 
unsuitable for this work. On all the media no difference in the two forms 
was noticeable, either in rapidity of growth or in luxuriance of growth. 

Hard potato agar. — A white, fluffy, aerial growth was produced in 
five or six days on hard potato agar. The growth was profuse. 

6 A comparison of the Phytophthora of ginseng was also made with nine other species of Phytophthora. 
The results of this study will be published in a subsequent paper. 



Phytophthora Disease of Ginseng 



§5 



Oat agar. — The growth on oat agar was profuse and was beneath the 
surface as well as at the surface, making a slightly yellowish, mealy growth. 

Corn meal agar. — On corn meal agar there was a slight growth, mostly 
subsurface. 

Bean pod plugs. — The growth on bean pod plugs was aerial as well 
as embedded in the tissues of the pod. The growth was white, but was 
less fluffy than on hard potato agar. 

Ginseng stems. — On ginseng stems there was a very scanty surface 
growth. 

KINDS OF SPORES PRODUCED ON VARIOUS MEDIA 

The kinds of spores produced and the time of appearance of these are 
shown in table 2 : 

TABLE 2. Kinds of Spores Produced on Various Media 







At the end of two weeks 






Organism 


On 

potato 


On 

oat 


On 

corn meal 


On 
bean pods 


On 

ginseng 
stems 


Phytophthora 
from ginseng 


Numerous 
conidia 


Oogonia, 
oospores, 
conidia 


Few 
conidia 


Few 
oogonia 


Numerous 
conidia, 
few oogo- 
nia, few 
oospores 


P. cactorum 
from Phyllo- 
cactus 


Numerous 
conidia 


Oogonia, 
oospores, 
conidia 


Few 
conidia 


Few 
oogonia 


Numerous 
conidia, few 
oogonia, few 
oospores 



At the end of six weeks 



Organism 


On 

potato 


On 

oat 


On 
corn meal 


On 
bean pods 


On 

ginseng 
stems 


Phytophthora 
from ginseng 

P. cactorum 
from Phyllo- 
cactus 


Numerous 
conidia 

Numerous 
conidia 


Conidia, 
few oogo- 
nia, numer- 
ous oospores 

Numerous 
conidia, 
few oogonia, 
numerous 
oospores 


Few conidia, 
few oogonia, 
few oospores 

Few conidia, 
few oogo- 
nia, few 
oospores 


Numerous 
oospores 
and conidia 

Numerous 
oospores 
and conidia 


Numerous 
conidia, 
few oogonia, 
few oospores 

Numerous 
conidia, 
few oogonia, 
few oospores 



It was found in several series of the above that, while the time of ap- 
pearance of the different spore forms may vary for the different strains 
of Phytophthora, eventually the same spore forms appear on a given 



86 



Bulletin 363 



medium. Oat agar and bean pods are especially favorable for the pro- 
duction of the sexual bodies. In the case of bean pods, the conidia appear 
mostly on the aerial growth, while the oospores are imbedded in the 
tissues of the pod. 




FlG. 9. MYCELIUM OF PHYTOPHTHORA, (a) FROM GINSENG, (b) FROM PHYLLOCACTUS 

The drawings were made from mounts of mycelium of the two oiganisms growing on oa.t agar, No con- 
stant difference can be noted 



Phytophthora Disease of Ginseng 



87 



COMPARATIVE MORPHOLOGY 

The morphological studies were made from cultures of the same age, 
grown on the same medium. No differences were noted in the mycelium 
of the two cultures (Fig. 9). In very young cultures there is a slight 
tendency to branch at right angles, but there is such great irregularity 
in the mycelium that such can hardly be taken to be a constant character. 

The conidia vary greatly in shape and size, but no difference between 
strains could be detected either when grown on the same or when grown 
on different media (Fig. 10). Over four hundred measurements were 
made for each form from cultures of different ages and grown on different 





Fig. 10. conidia of phytophthora, (a) from ginseng, (b) from phyllocactus 

The drawings were made from mounts of cultures of the two organisms growing on oat agar. Both 
drawings are made to the same scale 

media. The measurements most commonly obtained are the same for 
the Phytophthora from ginseng and for P. cactorum from Phyllocactus, 

34-5 X 27M- 

Inoculations were made on freshly disinfected ginseng roots in test 
tubes and the two forms were re-isolated from the inoculated roots. Pedi- 
greed single-spore cultures were then made, and conidia and oospores 
were again measured. 

The same differences appeared as were shown previously. Different 
workers have given different measurements, though working presumably 
with the same species. This is brought out in table 3, in which the 
measurements given by individual workers for the same species are 
presented. 



Bulletin 363 



TABLE 3. Showing Variation Given by Different Workers for 
Phytophthora cactorum 



Author 



Measurements of 

conidia 
( micromillimeters) 



Diameter of 

oospores 

(micromillimeters) 



Cohn and Lebert 

Hartig 

Schenk 

De Bary 

Sehroeter 

Osterwalder 

Himmelbaur 

Zimmerman 

Hori / 

Bubak 

Van Hook 

Author 



48 x 35-68 

^5-40 

* 

35-40 x 50-60-90 . . . 

35-40 x 50-60 

14.64-24.4 x 119.56 

Not given 

1 7-30 x 25-60 

30-50 x 50-60 

Abnormal 29 x 85 . 5 . 

15-25 x 15-120 

30-42 x 40-58 

34-5 *27 



20 (oogonium) 
16-24! 
24-30 . 
24 (oogonium) 
30-45 
None found 

26-28 

Not given 
Not given 



* Measurements cf conidia given by Schenk are as follows: " Die kleinsten derselben sind 5, die grossten 
3<> Theilstriche meines Zeiss'schen Mikrometers lang u'nd 4 bis 25 Theilstriche breit " 

f De Bary states that the oospores are in general from three-fourths to four-fifths the diameter of the 
oogonium. He gives the measurements of the latter as from 24 to 30 microns in diameter. The meas- 
urements given above for the diameter of the oospores were derived accordingly. 



It is thus shown that great variations may occur, apparently in the 
same species. De Bary, knowing of these variations as given by Lebert 




Fig. 11. the sexual process in phytophthora from ginseng 

Various stages are shown in the development of antheridium. oogonium, and oospores. Fertilization 
tubes are very evident in a number of cases 



Phytophthora Disease of Ginseng 



89 



and Cohn, by Hartig, and by Schenk, did not hesitate to place all forms 
in a single species. Likewise, Osterwalder (1906), notwithstanding the 
fact that his measurements do not agree with the others, does not con- 
sider this of sufficient importance to establish a new species. 




FlG. 12. THE SEXUAL PROCESS IN PHYTOPHTHORA FROM PHYLLOCACTUS 

More than four hundred measurements of oogonia were made for each 
form. Measurements of oospores taken from various media, and the 
cultures of different ages, show this spore form to be very constant. The 
measurements of the two forms are identical, being 27/i in diameter. The 
method of fertilization likewise does not differ in the two forms (Figs. 
11 and 12). 

A summary of the above comparisons, taken together with the results 
of the inoculations as shown previously, proves that the Phytophthora 
isolated from ginseng is identical with the culture marked Phytophthora 
cactorum (Cohn et Leb.) Schroeter isolated from Phyllocactus. 



LIFE HISTORY 

Careful studies of the fungus have been made in order to determine 
its various relations to its host and the morphological characters of the 
parasite itself. These studies have been made with fresh material from 
the garden and with pure cultures on various media. Plants which 
early in the spring show characteristic drooping usually exhibit no external 
evidence of the fungus. They show a slight shrinkage and browning of 
the tissues of the stem, and often the shrunken tissue appears water- 
soaked. If the stems are placed in a moist chamber for a day, a silvery 



<po Bulletin 363 

white coating of conidia appears, characteristic of Phytophthora. Mi- 
croscopical examination shows an abundance of the large ovate conidia of 
the pathogen. An excess of moisture in the chamber will force the fungus 
to the production of a large amount of mycelium with little conidial 
formation. In a few cases, by taking a microscope directly into the field 
the writer was able to find conidia on the surface of the stems. This 
was the case during a continuance of from two to three days of warm, 
muggy weather, accompanied by dews in the mornings. 

The conidia are spread by the wind or by other usual means of dis- 
semination; very often, no doubt, by the bodies of the workers while 
weeding. One who knows the conditions in a ginseng garden can readily 
understand how such is the case, since the weeders get down on their 
hands and knees. The rows, and the individual plants in a row, are so 
close together that it is almost impossible not to disseminate the spores 
when these are present. A spore falling on a healthy plant, under the 
right conditions of temperature and moisture, germinates, and within 
from four to six days infection becomes apparent. 

When a plant is infected in the tops, the fungus travels from the petioles 
into the main stem, through that, and into the root, where it rots the 
root. That the fungus travels downward is shown by the following 
experiment: On July 11, 19 13, twelve plants were inoculated in the 
tops with a pure culture of the fungus. Six other plants were used as 
checks. Half of the plants inoculated were injured by means of a flamed 
scalpel and the inoculum was placed inside the cuts; for the uninjured 
plants the inoculum was placed at the base of the petioles and covered 
with moist cotton. The check plants were treated in a similar manner, 
both as regards injuring half of them and covering the others with moist 
cotton, but the inoculum, of course, was not placed on them. Four 
days later (on July 15) the moist cotton was removed. On the same 
day all the plants injured and inoculated showed the characteristic drooping 
of the leaflets from the crotch of the plant. Within three days more 
four of the uninjured inoculated plants likewise showed the characteristic 
wilting. All the checks, whether injured or not, remained healthy. On 
July 20 it was apparent, by the hollowing out and discoloration of the 
stems, that the fungus was traveling downward. On pressing a stalk 
between thumb and forefinger, it was found that the ordinarily firm 
stalk felt hollow in the region of the discoloration. By marking the 
point of discoloration on the stem with india ink, it was ascertained that 
the fungus traveled about one-half to two-thirds centimeter each day, 
as indicated by the new limit of discoloration. On August 1 the stems 
were hollow for the entire distance to the ground. On that day one of 
the hollow stems was examined microscopically, mounts of tissue taken 



Phytophthora Disease of Ginseng gi 

from the inside being used, and oospores were found in great abundance. 
The oospores were most abundant near the origin of infection, and grad- 
ually diminished in numbers as the distance from this point increased. 
Thus all developmental stages of the fungus were found on the inside of 
the stem — oospores, oogonia, and mycelium. On August 7 the roots of 
some of the infected plants were completely rotted, and the crowns of 
others deeper in the soil were just beginning to rot. All the checks re- 
mained perfectly healthy during the entire time. 

Similar sets of inoculations were made on August 1 and August 15, 
with identical results. On inoculated plants that were slightly injured, 
100 per cent of infection was obtained in every case; on plants that were 
not injured, the percentage of infection was only from 25 to 50 per cent. 

In the early stages of the rot in the root, mycelium may be found in 
the tissues. In the summer of 19 13 an examination of a rotted root 
showed that one of the smaller rootlets contained numerous oospores. 
In the fall of the same year, an inoculated four-years-old root was placed 
in a test tube filled with sterile distilled water. An examination of the 
root ten days later showed numerous oospores. This experiment has 
since been repeated many times, but in all cases it has given negative 
results. In general, in the later stages of the rot the roots become soft 
due to the presence of soil organisms. When the roots are in this condition, 
nothing definite can be learned of the relation of the Phytophthora to the 
host. 

The preceding data show how the fungus starts in the tops by infections 
from conidia and travels down through the stem to rot the root. It was 
found, however, that in many cases of artificial infection of the top, if 
the root was some distance below the surface of the soil the fungus did 
not attack it. In order to determine this point more definitely eighteen 
plants were carefully transplanted at varying depths in the soil. The 
depths used were \, 1, 2, 3, 4, and 5 inches below the surface, three roots 
being planted at each depth. The depth at which roots are commonly 
found varies from f to 2 inches below the surface. The plants used as 
checks were likewise transplanted. After transplanting, sufficient time 
was allowed for the plants to establish themselves before inoculations 
were made. The plants were inoculated by slightly injuring the tops 
and placing the inoculum in the injured parts. As before, the fungus 
traveled down the stems, this being made evident by a discoloration 
and hollowing of the stems. In the case of roots \, 1, and 2 inches below 
the surface, all the roots rotted; of those planted 3 inches below the sur- 
face, one root rotted and two remained healthy; while of those planted 
4 or 5 inches below the surface, none rotted. The experiment was re- 
peated, but instead of transplanting plants at various depths the stems 



92 Bulletin 363 

of a number of plants were covered to various heights with soil. In these 
experiments, while the number of plants rotting at each depth did not 
correspond with the former, the experiments did agree in that they showed 
a correlation between the number of roots rotting and the depth at which 
they were planted. They also showed that in case of infections of plants 
of the same age and with stems of approximately equal length, the fungus 
took much more time to reach the root in the case of those stems that 
were deepest in the soil. These facts are suggestive in considering the 
control of the disease in the garden. 

It was supposed that the fungus might pass from the tops to the roots 
by conidia being washed down into the soil by rain water, and that those 
coming into contact with the tissues of the roots would produce infection. 
Numerous experiments were performed in order to determine this point, 
by planting roots at various depths in both heavy and light soils and 
drenching the plants with water containing conidia of the fungus. Con- 
flicting results only were obtained, and in no case were there any signs 
of infection unless the roots had previously been injured. Infection by 
this method, if it occurs at all in nature, is of relatively slight importance. 

The primary infection may start in the tops or in the roots. When 
the roots are first attacked, the spread of the pathogen may be just the 
opposite from that already described. Instead of traveling down the 
stem and rotting the root, the fungus rots the root and continues its course 
upward into the stem. Root infection may start from mycelium in the 
roots or from oospores that have wintered in the soil. Hartig (1875) 
has shown that oospores of the Phytophthora on beech, left in the ground 
for four years, are still capable of germination and infection of healthy 
plants. Repeated inoculations of ginseng roots placed in soil have 
shown that the fungus, after rotting the root, can travel upward (Fig 13). 
The following details of one series of these inoculations are offered: On 
June 15, 1 9 13, six roots of four-years-old plants were inoculated with a 
pure culture of the fungus by removing the soil from one side of each 
root, making a slight incision near the top, or crown, of the root with a 
flamed scalpel, and placing a bit of inoculum at the point of injury. Four 
check plants were injured in a similar manner, but were not inoculated. 
On July 1 7 all the tops of plants with inoculated roots showed a character- 
istic drooping and evidence that the roots were rotting. An examination 
proved this to be the case. The tops were carefully removed, and mounts 
were made from the inside of the stem at different distances from the 
crown of the root, which was the original point of infection. The following 
conditions were found: Two centimeters above the crown the stem was 
hollow, and mounts showed an abundance of oospores, oogonia, and 
mycelium. The tissues of the stem were brownish and water-soaked. 



Phytophthora Disease of Ginseng 



93 




FlG. 13. CHARACTERISTIC SYMPTOM OF GINSENG MILDEW 

The drying and shriveling of the stem near the crown of the root is an indication 
that the Phytophthora is spreading from the root upward 



94 



Bulletin 363 



Five centimeters above the crown the stem was firmer to the touch, though 
still showing an abundance of oospores, oogonia, and mycelium. The 
stem still presented a water-soaked appearance. Seven centimeters above 
the crown the stem was not hollow, but was still slightly discolored and 
mounts showed an abundance of mycelium. Evidently the mycelium at 
this point was not old enough for a differentiation into spore forms. Ten 
centimeters above the crown the stem was perfectly healthy and the 
microscopic examination showed no evidence of the fungus. In order to 
make sure that the mycelium and the spore forms seen belonged to Phy- 
tophthora, plantings from the interior of the stem from these various 
points were made on poured oat agar plates. The fungus obtained from 
these plantings was Phytophthora, identical with the fungus with which 
the roots had been inoculated. 



MORPHOLOGY OF THE FUNGUS 
MYCELIUM 

The mycelium of the fungus in culture is very characteristic and can 
be distinguished readily as a Phycomycete if examined carefully. Septa, 
as a rule, are absent, except for an occasional one in very old cultures. 

The branching is irregular, and consists of 
threads of varying diameter, as well as 
knoblike and button-shaped protuberances. 
The protoplasmic contents are granular, 
intermingled with oil globules and other 
larger bodies. The larger bodies are found 
for the most part in mycelium of an 
advanced stage. 

In plant tissue, especially in the root, 
the mycelium is scanty. The main branches 
are intercellular. Small branches are often 
seen to penetrate the cell walls. There is 
a constriction at the point of passage and 
a broadening out on each side of the cell 
wall (Fig. 14). In other words, the hyphas 
are reduced to mere threads in passing 
through the wall. Hartig (1882) describes 
and illustrates the haustoria of P. omnivora 
as spherical. Klebahn (1909:75) and Cole- 
man (1910:61), however, figure them as rather elongate and finger-like, in 
which case they agree closely with those of the Phytophthora of ginseng. 
In making mounts of affected stems, it was found in many cases that 
where the conidiophores arose in great abundance the mycelial branches 




FlG. 14. PASSAGE OF MYCELIUM 
FROM CELL TO CELL 

The mycelium is very much con- 
stricted at the point where it passes 
through the cell wall of the host. In B 
is shown a fragment of mycelium 
branching within the host cell. The 
drawing A was made with a 2-milli- 
meter objective, B with a 4-milhmeter 
objective 



Phytophthora Disease of Ginseng 



95 



had also penetrated within the cells. Morphologically the haustoria-like 
branches are not particularly specialized, since the conidiophores arise 
directly from them or from short inner branches extending from these 
swollen threads. 

CONIDIOPHORES 

The conidiophores arise from the mycelium within or between the 
epidermal cells. When about to produce conidiophores, the branches 
of the mycelium within these cells become slightly swollen at their tips. 
On emergence from the tissues, the swelling is immediately followed 
by a reduction in the 

diameter of the thread. JNtl To /f^—J, 

The reduced thread 
pushes or dissolves its 
way directly through 
the cuticle and the 
cell wall. In many 
cases the c o n i d i o- 
phores arise at the 
point of junction of 
two cell walls, but 
this is by no means 
always the case. The 
conidiophores, after 
passing through the Fig. 15. conidiophores of phytophthora from ginseng 

Small OOenill CT in the -^ Manner in which the conidia are borne on the conidiophores (16- 
* & millimeter objective;; (B) manner in which the conidiophores emerge 

Cell wall, may Swell from the tissue of- the host 

slightly and then grow into a long, almost straight stalk, which is 
usually not more than one-half or one-third the diameter of the hyphas of 
the mycelium from which it arose. The conidiophores never exhibit the 
peculiar swelling just back of the point where a conidium is bonie which 
is so characteristic of Phytophthora infestans. (Fig. 15.) 




^% ^ 



CONIDIA 

The conidia are ovate, with a prominent apical swelling, or papilla 
(Fig. 16). The papilla is lighter in color than the remainder of the 
cell, and apparently thinner also. At the larger rounded end of the spore 
the short broken attachment of the conidiophore is seen in some cases. 
The walls are smooth and hyaline. The double walls of the conidium, 
which indicate its sporangial nature, are quite evident, the inner one 
being much thinner than the outer. The contents are alveolate and 
granular. Often the center of the spore shows a large, clear spot, re- 



9 6 



Bulletin 363 



sembling a large vacuole. Conidial measurements, as pointed out pre- 
viously, average 34.5 by 27^. 

The conidium arises as a swelling. At first, and often until near 
maturity, it is almost globose in form. It gradually becomes ovate, 
the papilla being the last part of the spore to take its form. This appears 
about the time of maturity. In many instances, especially in cultures 
of considerable age, a tube is sent out from a little below the papilla, 





FlG. l6. GERM-NATION OF CONIDIA OF PHYTOPHTHORA CACTORUM 

Various stages in the germination of conidia by tubes, with the production of secondary and tertiary 
conidia, are shown above. Below are shown the germination of conidia by means of swarm spores, and 
the germination of swarm spores 



and at the apex of this another conidium is formed. The contents 
of the first conidium pass through the tube into the second conidium. 
The process may be repeated two or three times, giving the appearance 
of a chain of conidia. As a rule, each succeeding conidium is slightly 
smaller in size than the preceding one. 



Phytophthora Disease of Ginseng 



97 



GERMINATION of conidia 
The conidium is potentially a sporangium. It germinatss normally 
in one of two ways, either directly by the production of numerous germ 
tubes, or by the production of swarm spores. 

germination by germ tubes 

The most usual and most abundant type of germination observed is 
by means of germ tubes produced directly from the sporangium itself 
(Fig. 17). The number of germ tubes varies. The tubes are large and 




FlG. 17. GERMINATION OF CONIDIA OF PHYTOPHTHORA CACTORUM 

Various stages in the germination of conidia of Phytophthora cactorum from ginseng by means of 

germ tubes 

rather straight, with relatively few branches. They arise most commonly 
from the ends of the sporangium. Those arising from the proximal end 
of the sporangium ordinarily are fewer in number than those arising 
from about the apex. Moreover, the germ tubes from the proximal end 
commonly emerge directly from the point where the spore was attached 
to the conidiophore. At the apex the germ tube very seldom arises from 
the papilla, but usually from the side of the spore a short distance below the 
papilla. It is very characteristic of many of these germinations that the 



98 Bulletin 363 

germ tubes at the distal end arise in a whorl, or cluster, around the papilla. 
These germ tubes are densely granular, the contents of the sporangium 
passing out into them. The first evidence of loss of protoplasmic contents 
of the sporangium is the appearance of rather large vacuoles here and there 
through the spore. 

GERMINATION BY SWARM SPORES 

Germination by means of swarm spores (Fig. 16) was observed a number 
of times by making mounts from fresh cultures in drops of water in van 
Tieghem cells or on object slides. Swarming has also been seen on an 
object slide in a drop of water under a cover glass. The time for such 
germination varies. The first evidence of the presence of swarm spores in a 
sporangium is the movement of the protoplasmic granules in certain centers, 
or areas, in the sporangium. In some cases swarming is seen fifteen 
minutes after the conidia have been placed in drops of water. In other 
cases no signs of swarming are evident for from two to three hours. In 
examining a mount made for this purpose, there is often noticed a sudden 
and tremendous swarming in practically all of the sporangia. The swarm 
spores appear in the mount by hundreds, and a rapid review of the spo- 
rangia under low magnification shows swarm spores rolling out of nearly 
every one. It is a most exciting and extraordinary sight. 

The manner of emergence varies. Usually the swarm spores emerge 
singly and very quickly from the thin, narrow, papilla-like opening. 
The time usually required for the emergence of the mass of spores is 
from four to ten seconds. After emergence the spores are usually held 
together at the opening for from two to three seconds, after which they 
all swim apart in different directions. Often they do not congregate 
near the opening, but swim away as fast as they emerge. It often happens 
that for some reason two or three swarm spores do not emerge when the 
majority escape. In one case those left were noticed apparently trying 
hard for fifty-five minutes to get out, without success. At times, in 
their movements, they were at the very opening. It gave the impression 
that the opening where the majority of swarm spores escaped became 
closed again, and thus prevented the emergence of those left behind. 
In one particular case the spore came to rest and germinated inside the 
sporangium, the germ tubes extending through the walls of the sporangium. 
Very often two swarm spores, after emerging together, seem to stick 
together for two or three seconds, held by a fine protoplasmic thread 
or connection, after which each darts off by itself. 

SWARM SPORES 

The number of swarm spores in a sporangium varies with the size 
of the sporangium — the larger the sporangium, the greater the number 



Phytophthora Disease of Ginseng 99 

of swarm spores produced. The greatest number ever observed was 
thirty-six. Each swarm spore is provided with light-colored spots, 
or vacuoles, which are located nearer one end of the concave side. The 
concavity is near the smaller end of the pyriform swarm spores. It 
appears that here also are attached the flagella. These are two in number 
and of unequal size, varying in size from one and one-half to two times the 
length of the body of the swarm spores. 

After swimming for a time, the swarm spores come to rest, withdraw 
their flagella, become round, and germinate by sending out germ tubes. 
Germ tubes of considerable length are formed within a short time after the 
swarm spores have come to rest. Ordinarily one single germ tube is formed 
by each spore. 

It has always been a matter of interest to discover what determines 
whether germination is to be by swarm spores or by germ tubes. Different 
investigators have attributed the phenomenon to different causes. Klebahn 
(1909) cites a case showing that oxygen apparently is necessary for the 
emission of zoospores, while Coleman (19 10) states that the formation 
and emission of zoospores in a sporangium is clearly influenced by external 
factors, chief of which is a certain strength of light. Coleman states 
further that zoospores can be obtained in the Areca Phytophthora by 
suspending sporangia in water, placing them on the stage of the micro- 
scope, and illuminating them by means of the mirror and the condenser. 
This has been tried by the writer, not only for the ginseng Phytophthora 
but for the Areca Phytophthora as well, but for some unknown reason 
without success. In the same paper Coleman cites an experiment in 
which a number of cultures were kept in the dark and an equal number 
in the light. He draws no conclusions from the experiment, but from 
the results obtained one is led to believe that light is necessary for the 
formation of sporangia. In the writer's experience with Phytophthora 
cactorum from ginseng, this has not been the case. 

After numerous attempts to germinate conidia both from plants in 
the field and from growths on various media, the writer is inclined to the 
opinion that the age of the conidium has more to do with its manner 
of germination than external conditions. Conidia taken from young 
cultures — that is, cultures just beginning to form conidia — are more 
likely to germinate by swarm spores than are older conidia. In the case 
of conidia formed on the host, those having favorable conditions for 
germination soon after formation will germinate by swarm spores, while 
the others will germinate by germ tubes. 

sexual organs 
The antheridia and the oogonia form from the mycelium of the fungus 
when the fungus reaches a certain age. This varies with the medium 



ioo Bulletin 363 

on which it is grown. The antheridium and the oogonium mry arise 
as branches of the same thread or from different threads (Figs. 1 1 and 12), 
but always the threads are close together. The antheridium and the 
oogonium are terminal swellings of their branches. The formation 
of the two structures takes place simultaneously. In some cases the 
stalks bearing the antheridium and the oogonium are on the same side, 
and the antheridium then falls on the oogonial stalk. Under the micro- 
scope, such a condition may present the appearance that the oogonium 
has grown through the antheridium (Fig. 11). 

The antheridium at maturity is from elliptical to reniform in shape, 
and is cut off by a cross wall from the main part of the thread. The 
oogonium is globose and much larger than the antheridium, and is also 
cut off by a septum. The protoplasm in the early stages, in both the 
antheridium and the oogonium, is finely granular, with a number of 
oil globules varying in size. 

FERTILIZATION 

Preceding the formation of the oosphere a change takes place in the 
oogonial contents. The protoplasm becomes denser, and, together 
with the oil drops, collects in the center. After the oosphere has been 
formed in the oogonium, one may detect in some cases a fine, light- 
colored passageway extending from the antheridium to the wall of the 
oosphere (Fig. n). This is the fertilization tube. The passage of any 
contents into the oosphere from the antheridium has never been observed, 
though it undoubtedly takes place as an examination of later stages 
shows that the contents of the antheridium are less dense. But at 
this time the fertilization tube has disappeared. In one case on five- 
days-old oat agar culture numerous fertilization tubes were seen. The 
tubes were present also on the following day, but on the seventh day 
all signs of them had disappeared. In no case do all the contents of 
the antheridium pass into the oosphere in the act of fertilization, as is 
the case in many of the Phycomycetes. 

OOSPORE 

After fertilization has taken place the oospore gradually changes color, 
from hyaline to yellow or brown. During this change in color there is 
a gradual thickening of the wall of the oospore. The oogonial wall per- 
sists, but without any change. In most cases, however, in this species, 
careful focusing will show that the antheridium is superimposed on the 
oogonium. 

OOSPORE GERMINATION 

All attempts by the writer to germinate oospores during the year 19 12 
and a part of 19 13 met with failure, even though the oospores were taken 



Phytophthora Disease of Ginseng ioi 

from cultures almost a year old. Accordingly, in the fall of 19 13 it was 
decided to place the oospores under as nearly natural conditions as possible. 
Transfers of pure cultures of the Phytophthora isolated from ginseng 
and of Phytophthora cactorum from Phyllocactus were made on sterilized 
bean pod plugs in test tubes. At the end of two weeks these were examined 
and were found to contain numerous oospores. Some of the test tubes 
containing the oospore material were sealed with paraffin and covered 




FlG. l8. GERMINATION OF OOSPORES OF PHYTOPHTHORA CACTORUM 



with small rubber caps. From the remainder of the test tubes the bean 
pod plugs were removed and placed in small five-inch flowerpots con- 
taining sand. On December 2, 19 13, the covered test tubes and the 
pots were taken out of doors and buried an inch below the surface of 
the soil. On January 8 following, one of the pots was dug up. Small 
bits of the bean pod material containing oospores were placed in hanging 
drops of water to germinate. They were examined on several successive 
days, but no signs of germination were visible. On January 29 one of 
the covered test tubes was brought in and bits of material were placed 



102 Bulletin 363 

ki drops of water, but no signs of germination could be seen. Instead 
of discarding the remaining material, the test tube was partly filled with 
sterile distilled water. Mounts in van Tieghem cells and in drops of 
water were again made from this test tube on February 20. An exami- 
nation on the following day showed that many of the oospores had germi- 
nated. On the next day the remaining material was brought in and 
placed under water. At the end of two weeks no difficulty was encountered 
in germinating oospores from any of the material. The germination of 
oospores of the Phytophthora from both ginseng and Phyllocactus was 
identical. 

The oospores of the wintered material are granular, some being denser 
than others. In some cases the oogonial wall is broken or entirely gone 
and only the thick wall of the oospore is seen, in other cases the oogonial 
wall still persists. Just before germination the granular substance becomes 
denser near the periphery and the wall of the oospore takes on a striated 
appearance. Through a break in the wall a germ tube is sent out. The 
contents of the oospore gradually pass into this tube, which,' when it 
has attained a sufficient length, bears a conidium. More than one 
conidium may be borne, as is the case with ordinary conidiophores. As 
germination proceeds, the striations on the oospore wall disappear and 
the wall itself diminishes in thickness. Various stages in the germination 
of the oospores are represented in figure 18. 

The conidia thus produced have been seen to send out ordinary germ 
tubes, as well as to break up into swarm spores. 

CONTROL 

The various methods of control of Phytophthora of ginseng fall 
under the following heads: (1) spraying with fungicides; (2) removal of 
diseased plants or parts of plants; (3) deep planting; (4) crop rotation; 
(5) sterilization of the soil; (6) drainage. 

SPRAYING 

As has been pointed out, the most favorable time for infection is very 
early in the spring, just as the plants are pushing through the soil. At 
this time the plant tissues are succulent and tender, and the temperature 
and weather conditions, as a rule, are most favorable for spore germination 
and infection. In order to prevent this early infection of the tops, a 
fungicide should be applied as the plants are pushing through the soil, 
and the application should be continued at intervals until all the plants 
have made their appearance. Spraying after this period will depend 
on weather conditions and on the amount of growth that the plants have 
made since the last application. Spraying should be done before rainy 
periods, and all the new growth should be covered with the fungicide. 



Phytophthora Disease of Ginseng 103 

Various fungicides, such as lime-sulfur solution, bordeaux mixture, 
and bordeaux mixture with arsenate of lead, have been tried for two 
seasons. Lime-sulfur solution in some cases causes injury to the foliage. 
As between bordeaux mixture with and without the addition of arsenate 
of lead, the former has been found to be the more satisfactory. Arsenate 
of lead seems to improve the adhesive quality of the mixture, which remains 
on the foliage longer when this is used. The fungicide employed should 
therefore be bordeaux mixture 3-3-50, to which has been added two pounds 
of arsenate of lead for every fifty gallons of mixture. 

REMOVAL OF DISEASED PARTS 

It has been found that if the diseased tops — that is, those that show 
a wilting and drooping — are removed just as soon as they are noticed, 
the fungus will be prevented from traveling down the stem. When the 
root is believed to be affected, it should be carefully removed from the 
bed. It is a good practice to disinfect the soil with a fungicide at the place 
from which the root has been removed. Formaldehyde, one part to 
twenty-five parts of water, or copper sulfate, one pound to ten gallons 
of water, is a good solution for this purpose. 

DEEP PLANTING 

During the summer of 191 1, in a garden three-quarters of an acre 
in size, almost every plant was lost through attacks of Phytophthora. 
The disease seemed to start in the tops, and in a short time nearly every root 
in the garden was affected. There were, however, about a dozen plants 
scattered throughout the garden which did not seem to be affected. These 
came up again the following spring, and on examination it was found 
that without exception the roots of the plants not attacked were planted 
at least four inches below the surface of the soil. From artificial infections 
recorded in the preceding pages, it is seen that the fungus can travel 
down the stem and rot the root. When the crown of the root is several 
inches below the surface of the soil, however, there is less likelihood that 
the root will rot. In the case of the potato Phytophthora, hilling up 
of the rows has been suggested as a means of reducing the rot of the tubers ; 
but the method appears to be impracticable, since it causes a consider- 
able reduction in yield. In the case of ginseng, the roots are left in the 
ground for five years or longer. 

ROTATION OF CROPS 

A garden once affected with Phytophthora cannot be again used for 
ginseng for some years. A number of growers whose land had become 



104 Bulletin 363 

infected allowed the land to lie fallow for two years. They then planted 
seed, and the seedlings were attacked to a considerable extent by the 
disease. Hartig (1882) showed that the oospores can live for a number 
of years in the soil. Financially the grower cannot afford to let his land 
lie fallow for a period of years, since it is almost impossible to move 
the shade. The writer therefore suggests that a rotation with some 
other crop, requiring the same conditions of shade, be practiced. Golden 
seal (Hydrastis canadensis) is a good plant for this purpose. A number 
of inoculation experiments have been made with the ginseng Phytophthora 
on golden seal, and in no case has there appeared any evidence of infection. 

STERILIZATION OF SOIL 

Where it is not desirable to practice rotation of crops, the sterilization 
of soil by means of steam will prove of value. The steam pipe method 
and the inverted pan method have been tried. The inverted pan method 
is by far the more satisfactory, because of the greater ease with which 
the pan is handled and because less of the steam is lost than in the pipe 
method. 

The pan should be of galvanized iron, of a width equal to that of the 
beds in the garden, a length of ten or twelve feet, and a depth of from 
five to seven inches. The sides should be provided with sharp edges, 
which are forced down into the soil. The soil is prepared as for planting. 
It is necessary to have a pressure of from seventy-five to one hundred 
pounds for forcing the steam into the soil. The length of time required 
for each pan will vary with the kind of soil, owing to the fact that steam 
penetrates a sandy soil with greater ease than one of clay. Depending 
on these conditions, the time will vary from twenty to forty minutes. 

DRAINAGE 

When plants are growing naturally in the forest, the excess water 
in the soil is removed by the roots of trees and shrubs. Under culti- 
vation some artificial means of removing the excess of water from the 
beds must be employed. In one experiment it was found that a much 
greater abundance of oospores was produced when the root was placed 
in an abundant supply of water. Vegetable rots in general are favored 
by an abundance of moisture. It is therefore suggested that some type of 
underground drainage be employed to carry off the excess of water in the 
soil. Ordinary hard-burned clay tiles have proved most effective and 
permanent for this purpose. The depth, interval, and size of the drains 
must vary with the character of the soil and of the subsoil and with the 
amount of rainfall. In general the drains should be placed at a depth 
of from two to three feet in sand and gravel, and from one and one-half 



Phytophthora Disease of Ginseng 105 

to two feet in clay. Where possible a tile drain should be placed under 
the center of each bed, or the drains may be placed at intervals of from 
six to eight feet. The size of the tile depends on the volume of water 
to be carried. In the ginseng-growing sections of New York State a 
three-inch tile has been found satisfactory. 

BIBLIOGRAPHY 
Bary, Anton de 

1876 Researches into the nature of the potato-fungus — Phytoph- 
thora infestans. Roy. Agr. Soc. England. Journ. 2:12: 
239-269. 

1881 Zur kenntniss der Peronosporeen. Bot. ztg. 39:585-595, 

601-609, 617-626. 
Coleman, L. C. 

1910 Diseases of the Areca palm. I. Koleroga. Mysore State Agr. 
Dept. Myc. ser., Bui. 2:1-92. 
Hanai, I. 

1900 [Japanese title.] On the culture and curing of the Idzumo 
ginseng. Cent. Agr. Exp. Sta. (Japan). Rept. 8:28-29. 
Hartig, Robert 

1876 Die buchencotyledonen-krankheit. Zeitsch. forst.- u. jagdw. 
8:117-123. 

1882 Phytophthora omnivora (Phytophthora Fagi und Peronospora 

Sempervivi) . Lehrbuch der baumkrankheiten, p. 42-46. 
Hook, J. M. van 

1904 Diseases of ginseng. Cornell Univ. Agr. Exp. Sta. Bui. 
219 : 168-174. 

1906 A disease of ginseng due to Phytophthora. Spec, crops n. s. 

5:94- 
Hori, S. 

1907 A disease of the Japanese ginseng caused by Phytophthora 

cactorum (Con. et Leb.) Schrot. Imp. Cent. Agr. Exp. Sta. 
(Japan). Bui. 1:2:153-162. 
Jartoux, Father 

1 7 14 The description of a Tartarian plant, called ginseng; with an 
account of its virtues. . . . Taken from the tenth 
volume of letters of the missionary Jesuits. Roy. Soc. 
London. Philosophical trans. 28:237-247. 
Klebahn, Heinrich 

1909 Krankheiten des flieders, p. 1-75. 
Lebert, H., and Cohn, F. 

1870 Ueber die faule der cactusstamme. Beitr. biol. pflanz. 1 : 51-57. 



106 Bulletin 363 

Osterwalder, A. 

1906 Die Phytophthorafaule beim kernobst. Centbl. bakt. 2 : 15 1435- 
440. 
Saccardo, P. A. 

1888 Phytophthora cactorum (C. et L.) Schroet. vSyll. fung. 7:238. 
Schenk, August 

1875 Sitzungsberichte der Naturforschenden Gesellschaft zu Leipzig. 
Bot. ztg. 33:690-693. 
Schroeter, J. 

1889 Gattung Phytophthora De Bary. Krypt.-fl. Schlesien 3:235- 

236. 
U. S. Department of Commerce, Bureau of Foreign and Domestic 
Commerce 
1914 The foreign commerce and navigation of the United States 
for the year ending June 30, 1913, p. 394. 
U. S. Secretary of the Treasury 

1822 Letter from the Secretary of the Treasury, transmitting state- 
ments shewing the commerce and navigation of the United 
States for the year ending the 30th September, 182 1, p. 73. 
Whetzel, H. H. 

19 10 The mildew of ginseng caused by Phytophthora cactorum (Leb. 
& Cohn) Schroeter. Science n. s. 31:790-791. 
Whetzel, H. H., and Rosenbaum, J. 

19 1 2 The diseases of ginseng and their control. U. S. Plant Indus. 
Bur. Bui. 250: 17-19. 



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